This invention relates generally to gas turbine engines, and more specifically to methods and apparatus for machining gas turbine engine components.
Accurate manufacturing of a component may be a significant factor in determining a fabricating time of the component. Specifically, when the component is a gas turbine engine blade, accurate manufacturing of the blade may be one of the most significant factors affecting an overall cost of fabrication of the gas turbine engine, as well as subsequent modifications, repairs, and inspections of the blade. For example, at least some known gas turbine engines include a compressor for compressing air which is mixed with a fuel and channeled to a combustor wherein the mixture is ignited within a combustion chamber for generating hot combustion gases. At least some known compressors include a rotor assembly that includes at least one row of circumferentially spaced rotor blades. Each rotor blade includes an airfoil that includes a pressure side, and a suction side connected together at leading and trailing edges. Each airfoil extends radially outward from a rotor blade platform. Each rotor blade also includes a dovetail that extends radially inward from a shank coupled to the platform. The dovetail is used to mount the rotor blade within the rotor assembly to a rotor disk or spool.
During operation, a pressure differential is created between the compressor blade pressure side and the compressor blade suction side which may result in an undesirable leakage flow between the upstream and downstream portions of the rotor. One such possible leakage path may form at an interconnection between each rotor blade and the rotor disk, where a gap may be defined between a blade base member, usually a dovetail design, and a rotor disk groove in which the rotor blades are carried. Accordingly, in at least some gas turbine engines small diameter seal wires are inserted between the blade platform and the outer periphery of the rotor disk to facilitate sealing the upstream and downstream areas at the interconnection formed between each rotor blade and the rotor disk. The seal wires are split and as such, may expand in a radial direction when subjected to centrifugal force. Seal wires facilitate minimizing leakage gas flow from the high-pressure region of the flow path to the low-pressure region, and thereby maintain the maximum mass flow of the gas flow stream to maintain the operating efficiency of the engine.
At least some known methods of fabricating a seal wire groove include fabricating a machining assembly that includes a plurality of individual components permanently coupled, for example by bolting the components to the assembly, to enable a groove to be machined in a specific set of compressor blades. For example, during fabrication, the machining assembly is installed in a milling machine and a plurality of test cuts are performed on the blade to verify the alignement of the retainers. The seal wire groove is then machined into the compressor blades. The machining assembly is then removed from the milling machine and the individual components are then unbolted from the machining assembly and a second set of components is bolted. The machining assembly is then re-installed in the milling machine and a plurality of test cuts are performed on the blade to verify that the machining assembly is properly aligned for the second time. A seal wire groove is then machined into a second set of compressor blades installed on a second compressor rotor section. This process is repeated until all the compressor blades for each compressor rotor section have been machined.
Removing the machining assembly from the milling machine and re-installing separate components for each set of compressor blades is a relatively labor intensive process since each holding fixture must be installed on the milling machine prior to cutting the seal wire groove in the next set of blades. Additionally, an increased quantity of milling cutters are used to perform the test cuts and to machine the seal wire groove. Since the method for cutting a seal wire groove is relatively complex, at least one known manufacturer machines a plurality of seal grooves without changing the holding fixture to faciliate reducing costs of fabrication. Accordingly, the manufacturer may often produce a quantity of blades that is in excess of the quantity desired by the customer.